The present invention relates generally, as indicated, to a monitor system and method and, more particularly, to a monitor system and method for detecting whether successive events occur at their proper positions in a process, for example, to stop the process and/or to issue a warning when an event is missed. The invention also is particularly directed to a monitor system for a rip detector for conveyor belts and the like.
In large endless non-metallic conveyor belts used to convey bulk material, there is a possibility of encountering a rip in the belt, for example, by a sharp object dropped thereon at the loading station. It is desirable promptly to detect such rips and, preferably, to shut down the conveyor belt upon such detection, thereby minimizing damage to the belt. One such conveyor belt rip detector is disclosed in U.S. Pat. No. 3,792,459. In such rip detector plural antennas, which may be single electrical conductors, are embedded in the belt transversely to its length at spaced-apart locations in the belt. An electrical signal is coupled by respective antennas from a transmitter to a receiver as the belt moves and the respective antennas pass in capacitive coupling relation with the transmitter and receiver at a rip detector station. The electrical signal charge capacitively induced in each of the unbroken antennas is, thus, transmitted to the receiver and is sensed by detector circuitry thereof. However, a broken antenna, for example at a place where the belt has been ripped, will not couple the transmitter signal through to the receiver, and the detector circuit, then, senses the same as an indication of the occurrence of a rip condition. The detector circuit in such patent is operative after the lapse of a predetermined time period, which corresponds to the time required for the passage of a given number of broken antennas past the rip detector station without the coupling of the transmitter signal to the receiver, to produce a distinguishable output that activates an alarm and/or deactivates the conveyor belt drive.
The undesirable inaccuracy in such prior rip detector due to the long waiting period to see whether after an antenna has been missed the next antenna is detected means that a rather long and expensive to repair rip may occur before the conveyor is shut down. Moreover, since such conveyor belts are known to stretch, for example on the order of about 20%, during useful life, the indicated waiting period must be adequately long to accommodate the lengthened belt, thus further reducing the accuracy of detection and promptness of shut-down.
Accordingly, it would be desirable to provide a conveyor belt rip detector system that has improved accuracy enabling the same to detect a rip promptly upon occurrence thereof, even as conditions, such as the belt length, change.
Another disadvantage with such prior rip detector is the lack of diagnostic capability. When a shut-down of the conveyor belt occurs, for example, due to a failure in the rip detector, rather than a rip in the conveyor belt, the time wasted diagnosing the failure can be expensive in terms of lost production time of the conveyor belt. Alternatively, if the conveyor belt were operated without rip detector protection, for example while a rip detector failure is diagnosed, the unprotected belt may be completely ruined by a continuous rip that shoud have been detected by a properly operating rip detector.
Therefore, it would be desirable to facilitate diagnosing failures in the rip detector system itself to minimize down time and/or unprotected operation of a conveyor belt.